1. Field of the Invention--
The present invention relates generally to injection sites for use in the injection of fluids into the body. More particularly, the invention concerns a subcutaneous access site for repeated intermittent vascular and spinal injection or continuous infusion of drugs and fluids.
2. Discussion of the Prior Art--
Blood sampling, drug delivery and fluid replacement frequently require repeated access to the vascular system of the body. Typically, access to the vascular system is gained using a hypodermic syringe. Repeated injections by means of repetitive punctures is obviously undesirable, especially in fragile vessels or difficult to reach body regions. For this reason, various types of subcutaneous access sites have been devised in the past.
One relatively early prior art implant device for the injection and withdrawal of fluids is disclosed in U.S. Pat. No. 3,310,051 issued to Schulte. A later U.S. Pat. No. 4,190,040, issued to Schulte, discloses a resealable puncture housing for surgical implantation. This latter device is adapted to receive repeated hypodermic punctures through the skin and into the housing of the device. A subcutaneous peritoneal injection catheter is disclosed in U.S. Pat. No. 4,405,305 issued to Stephen et al.
In using subcutaneous access devices for the injection of drugs, great care must be taken to insure that the hypodermic needle punctures the septum of the device and is not deflected away by the supporting structure of the device so that the drug is accidentally introduced into the subcutaneous pocket within which the device is located. With certain drugs, such as chemotherapeutic drugs, this type of extravasation can be extremely serious. In a similar vein, certain prior art devices tend to leak around the puncture site, or around the internal reservoir of the device, particularly under conditions of back pressure experienced during the injection step. This leakage can also result in a dangerous drug or a caustic fluid accidentally reaching the subcutaneous implantation pocket and the body areas surrounding the injection site.
In certain of the earlier prior art subcutaneous access devices the basic design and choices of construction materials were poor. This resulted in ineffective sealing about the needle and substantial fluid leakage of the septum after relatively few punctures. Additionally, dangerous material degredation was frequently observed as a function of time. Further, the septum, or injection membrane of the prior art devices, was typically supported in a manner which allowed axially directed stretching of the membrane which worked against, rather than improving, the resealing characteristics of the septum after puncture by the needle of the syringe.
Other drawbacks of the prior art subcutaneous access devices include difficulty of surgical implantation, patient discomfort and errosion of interface tissue as a result of the bulk and configuration of the devices. Additionally, in many instances, the prior art devices were constructed of rigid plastic or metal components which markedly contributed to patient discomfort and tissue damage.
The device of the present invention uniquely overcomes the aforementioned drawbacks of the prior art devices by providing a novel subcutaneous injection site which is specially designed to provide superior septum resealing characteristics and to provide immediate feedback to the care giver if the needle misses the septum target area.